function [ ] = mx_eyelink_data_start( )
%MX_EYELINK_DATA_START Switches tracker to Record mode, enables data types for
% recording to EDF file or sending to link. These types are set with a bitwise 
% OR of these flags:
%
% RECORD_FILE_SAMPLES (1) - only active if file open.
% RECORD_FILE_EVENTS (2) - only active if file open.
% RECORD_LINK_SAMPLES (4) - accept samples from link.
% RECORD_LINK_EVENTS (8) - accept events from link.
%
% Remarks:
% If <lock> is nonzero, the recording may only be terminated through 
% stop_recording() or eyelink_data_stop(), or by the Abort menu (‘Ctrl’ ’Alt’
% ’A’ keys on the eye tracker). If zero, the tracker 'ESC' key may be used to
% halt recording.
%
% Parameters:
% flags 	Bitwise OR of flags to control what data is recorded. If 0,
% recording will be stopped.
% lock 	If nonzero, prevents 'ESC' key from ending recording.
% Returns:
% 0 if command sent OK, else link error.
%----------------------------------------------------------------------------
% Copyright Eduardo Aponte 2013
% aponteeduardo@gmail.com